During the past several years there has been a significant increase in the use of the one visit procedure (N2) for the treatment of endodontics patients by dental practitioners in the United States. On the basis of scientific evidence the N2 method is not taught in any dental school in the United States; however, the evidence available is difficult to interpret since there is an abvious absence in the literature of studies that directly compare the N2 method with the conventional method which is accepted in the United States. Initial studies which compared the reaction of infected periapical tissues to each method of treatment have indicated a statistically significant adverse tissue reaction to the N2 method of treatment. The gutta percha - Grossman's sealant preparations also caused a moderate to severe chronic inflammatory response which lasted throughout the observation period (6-12 mos.). The proposed study will compare the periapical tissue response after 6 months to ZOE; ZOE-paraformaldehyde; medical grade silastic and the new N2 formula filed with A.D.A. Council on Dental Therapeutics. N2 treated animals will be compared with conventional treated animals after two years. In addition, the efficiency and effectiveness of the rat tail file will be compared with the K-type and Hedstrom files with respect to debridement and canal preparation.